WebUI: swap paper-dropdown-menu out for md-select.

chrome/browser/resources/md_user_manager/create_profile.js

Index: chrome/browser/resources/md_user_manager/create_profile.js
diff --git a/chrome/browser/resources/md_user_manager/create_profile.js b/chrome/browser/resources/md_user_manager/create_profile.js
index a9a15572c21bb760336d1837012acc1a42841aac..b56b3d1cb6ec6f5a54692f2dad95fcaa091775f3 100644
--- a/chrome/browser/resources/md_user_manager/create_profile.js
+++ b/chrome/browser/resources/md_user_manager/create_profile.js
@@ -396,6 +396,15 @@ Polymer({
         this.isSupervised_, '', custodianProfilePath);
   },
 
+  /**
+   * Handler for a change in the supervised account dropdown.
+   * @param {!{target: HTMLSelectElement}} event
+   * @private
+   */
+  onAccountChanged_: function(event) {
+    this.signedInUserIndex_ = parseInt(event.target.value, 10);
+  },
+
   /**
    * Handler for the 'import' event fired by #importUserPopup once a supervised
    * user is selected to be imported and the popup closes.